In a hard-hitting statement, Mr Nesbitt atacked the DUP for not following the Ulster Unionists out of the Executive but said he would not be “deflected”.

He added: “It is equally remarkable that he can not agree with me that enough is enough and take a principled stand”.

A subsequent political furore over the chain of events has cast serious doubts over the future of devolved political institutions in the North. Prime Minister David Cameron Secretary of State for Northern Ireland, Theresa Villiers are due to meet with the DUP today.

The controversy was sparked when PSNI Chief Constable George Hamilton said the PIRA still exists and some members, along with a group styling itself Action Against Drugs, were involved in the murder of Mr McGuigan, a 53-year-old father-of-nine, earlier this month. The problem for Peter Robinson is that there is no battlefield under his command.

Peter Robinson, who has been on holiday, branded the UUP decision irrational, illogical and based on “political expediency” rather than principle.

Last week, his party called for Sinn Fein – once the political wing of the IRA – to be thrown out of Northern Ireland’s government.

Robinson said on Monday that the current crises – which include ongoing disagreements between the two sides over parades, flags and social welfare reform – represented the most unsafe set of circumstances in nearly a decade and had the potential to bring down the Assembly if they are not resolved.

The former IRA man was shot dead in east Belfast last month.

Mr Robinson said he accepted a police assertion that IRA members were involved in the murder of Mr McGuigan and that some IRA structures remain in place.

Police believe the killing was a revenge attack by republican associates of IRA commander Gerard “Jock” Davison who was gunned down in May.

Martin McGuinness has urged David Cameron not to meet Democratic Unionist demands to suspend the Northern Ireland assembly over the crisis threatening power sharing in the region.

Northern Ireland’s government will not sit for the next four weeks to facilitate all-party talks to save the power-sharing executive threatened by a crisis over an IRA-linked murder, Irish Prime Minister Enda Kenny said on Tuesday.

Mr Beattie said, “What political party anywhere in the United Kingdom is allowed to decide policy on education or agriculture, vote on policies affecting our everyday lives while at the same time retaining direct links to a proscribed organisation such as the IRA”.

His recommendation to pull out of the five-party Executive was unanimously backed by 90 members of the UUP’s governing body during a vote on Saturday.